Year	Percent
1991	21.7
1992	21.18
1993	20.54
1994	19.9
1995	19.27
1996	18.68
1997	18.08
1998	17.48
1999	16.82
2000	16.26
2001	15.05
2002	13.36
2003	12.74
2004	14.06
2005	14.02
2006	14.38
2007	15.01
2008	17.44
2009	15.27
2010	13.51
2011	13.37
2012	12.86
2013	13.02
2014	12.68
2015	13.53
2016	12.43
2017	12.49
2018	11.79
2019	10.89